(1) Field of the Invention
This invention relates to composite sucker rods for wells and more particularly to fittings and couplings for the sucker rod.
(2) Description of the Related Art
Oil field wells are often over 20,000 feet deep. Sucker rods, which are usually manufactured in lengths of about 25 feet, 30 feet, or 37 feet are joined together by means of coupling to form a rod string which extends the length of the well casing. In a typical well this rod string connects the horse head to the piston in the pump at the base of the well. With each stroke of the piston, oil is forced up to the surface through the annulus between the rod and tubing.
Normally a sucker rod string will be designed of certain material of some certain diameter so that it has a design working load. I.e., the diameter of the rod, the particular alloy of the steel to be used in the fittings and the dimensions of the fitting will all be designed for a particular working load of the string. A typical design working load for a string of this type would be 20,000 pounds. The design working load will vary with many elements, such as well depth and pumping rate.
In recent years, composite rods have been used to form the individual sucker rods of the string. The composite rods exhibit many characteristics which make them superior to steel rods. In using composite rods, the end fittings and the couplings to couple one length of sucker rod to the next have caused problems.
In this specification, the term "composite rods" should not be equated to glass fiber rods. In the technology today the composite rod consists typically of high strength fibers of glass or some other material which are bonded together into a single rod. Those having ordinary skill in the art will recognize that these fibers may be of carbon or aromatic polyarmide (commonly known by Du Pont's Trademark KEVLAR) or other substance. The term "composite rods" is used herein to indicate a manufactured material having high tensile strength.
Normally the sockets and couplings by nature will be larger in diameter than the rods which they connect together. However, it is desirable that they not be excessively large otherwise they will form an obstruction to the flow of fluid (oil) in the annulus between the rod string and the tubing. The limit to which the diameter of the socket and coupling can be reduced is limited inasmuch as normally the strength of the socket and coupling in tension is equal to or greater than the strength of the rod.
The joining of the composite material in rod form to the steel of the socket has been a problem.
Traditionally and according to API (American Petroleum Institute) specifications the sucker rods in oil wells will have a pin on each end of the rod. The rods will be connected together by a coupling unit which is typically less than 12 inches in length and has a box or female connection on each end thereof.
Also the pins are threaded to the sockets. The particular threads by which the pins are threaded to the sockets are designed and called pin threads. Tables are available through the API whereby the total longitudinal force exerted by a given torque upon the threads for any particular diameter of pin and socket is known.
Prior connections of the composite rod to the steel socket included placing the rod directly within the socket, and holding it in place with epoxy. The stretching of the rod led to the breaking up and failure of the epoxy. Subsequently, there would be nothing to hold the rod in place. Its movements would then be erratic. Gluing the rod into the socket directly also made repairs more difficult on either of them.
Prior attempts to hold a composite rod within a tapered sleeve by the use of wedges has met with failure when the wedges were not adhered to the rod. I.e., to attempt to connect the rod within a socket as is shown with steel cable in CARLSON, (identified below) have not been suitable for a composite rod.
Likewise, attempts to insert a composite rod into a socket with a tapered form in the socket and to pour epoxy or other resins or liquid composite material into the blind hole around the rod have not been satisfactory. The main problem has been the inability to form a good bond between the material forming the expansion cone and the rod itself.
The following patents are of record in the parent application identified above.
______________________________________ U.S. Pats. BUTLER ET AL 991,196 SHAFFER 1,384,489 CLARKE 1,392,480 TIBBETTS 2,659,062 HOWARD 3,168,340 YONKERS 3,698,749 CARLSON 4,205,926 SABLE ET AL 4,249,831 PRIDY 4,329,124 FISCHER 4,430,018 PETTERSON ET AL 4,497,866 French Patents BESSONNEAU 1,364,098 PLASTIMO 2,410,186 ______________________________________
Applicant believes the Examiner would consider anything of record in the parent application to be relevant and pertinent to the examination of this application. In addition applicant is aware of the PAGAN, U.S. Pat. No. 4,585,368, issued Apr. 29, 1986 on an application filed Sept. 17, 1984.
PAGAN discloses a sucker rod fitting where a plurality of wedges are formed in the socket and inserts are placed between the wedges and the rod. Column 4, line 20 states that the inserts may be fabricated of any suitable material including metal. However, PAGAN prefers molding them of thermoplastic or thermosetting material such as polysulfone, polyethersulfone, polyetherimide or polyphenylene sulfide filled with fibers of glass, graphite, or carbon; or phenolic resin, epoxies, or polyester.
PAGAN also describes that a biasing force may be applied to the wedges to hold them firmly in place while the wedges are adhered to the rod. This biasing force described in column 6, line 22 is approximately 40 pounds. PAGAN in FIGS. 9, 10, and 11 disclose a passage way extending through the pin end of the coupling (PAGAN describes his coupling as having a pin end rather than a socket end). This passage way through the pin end has in it rods with a disk. This disk can be used to press or bear against the inserts with multiple tapers on them to apply the biasing force (about 40 pounds) to the inserts while the adhesive sets.